1. Field
The present application relates to tires and in particular to a device to limit the effects caused by a rapid loss of tire pressure.
2. Description of Related Art
Tires of all types are subject to various forms of attack inflicted on them by roads: defects in the road surfacing, the presence of foreign bodies which can sometimes prove to be very aggressive, obstacles of all kinds, etc. This being the case, the risk of a tire becoming punctured during use is present everywhere and under widely varying circumstances. Such punctures may lead to very rapid loss of pressure.
In the case of tires of the passenger vehicle type, this problem has been the subject of numerous technological developments. For example, tire/rim assemblies have been developed (see, in particular, U.S. Pat. No. 6,092,575, U.S. Pat. No. 6,418,992, U.S. Pat. No. 5,634,993 and U.S. Pat. No. 5,785,781) which, in the event of a loss of pressure, allow the user to continue his journey at least over a minimal distance. In general, deflation warning devices are provided in vehicles equipped with such assemblies so as to alert the user to a loss of pressure. Tires in which the structure, particularly in the side walls, is strengthened in order to allow them, even in the deflated state, to carry a load substantially equivalent to their nominal load without any appreciable change in performance, at least over a minimal distance, are also known.
However, not all vehicles, and especially not all vehicles of the heavy goods vehicle type, are currently equipped with such assemblies or tires. In order to make the effects of a puncture on tires of a conventional type as little instantaneous as possible, the prior art has proposed solutions which, for example, involve placing inside each tire of the conventional type another tire of suitable dimensions so that when the tire is punctured or loses pressure, the inner tire serves to support the outer tire. Nonetheless, it remains the case that the difference in behavior between the situation in which the initial tire is inflated and the situation in which the tire is supported by an inner tire is very great (it no longer being the outer tire working but the inner tire) and this may prove to be something that the driver of the vehicle finds difficult to adapt to in such situations.
Devices placed inside the tire and which, while not being inflated during normal use, can reduce the loss of pressure in the tire when the latter is punctured are also known. The document published under reference US2002/0121325 describes a device such as this. The device comprises a toroidal tube the dimensions of which are small by comparison with the volume of the tire cavity in order to avoid as far as possible any interactions between the tire and the tube during normal operation (that is to say when the tire is inflated), this tube being provided with at least one opening to place the cavity delimited by the tube in communication with the cavity of the tire in which the tube is positioned. If the tire is punctured, the inflation pressure in the cavity delimited by the tire and the toroidal tube escapes whereas because the said tube has only a small opening, its pressure remains practically unchanged at least for long enough for the driver to get to a repair facility. The action of the pressure in the tube, the dimensions of which are appropriate to those of the tire in which it is placed, presses it against the beads of the tire with the effect of holding the beads against the rim flanges and limiting the loss of pressure in the tube.
However, while it is easy to have the tube pressed firmly against the beads in a tire with an aspect ratio (cross-sectional height/cross-sectional width) of at least 0.80, the same is not true of a tire of the kind known in English as a “low ratio” tire, that is to say in which the aspect ratio is below 0.80, because the tube, as it inflates, of necessity adopts a purely pneumatic equilibrium shape which tends to distance the said tube from the walls of the tire which it is supposed to push away in order to press them against the rim.
Finally, this tube does not make it possible to prevent the tire behavior from changing because there is a lag of some duration between the start of the loss in pressure from the cavity formed between the tire and the tube and the moment at which the tube is itself called upon to act as a support. Finally, when the tire is supported by the inflated inner tube, the geometry of the tire is quite substantially altered by comparison with the geometry that this same tire adopts when it is inflated and not punctured.